Snake my_turn_in puzzle implementation in Haskell

SnakeMyTurnIn.hs

-- Snake my_turn_in puzzle implementation
--
--   The direction argument accept an Ordering value where GT is
--   :forward, LT is :backward and EQ is :same.
--
--   Problem definition can be found in:
--     https://github.com/budu/Puzzles

myTurnIn :: (Ord a, Integral a) => a -> a -> Ordering -> a -> a
myTurnIn _  _  _ 1 = 0
myTurnIn p1 p2 d s
    | mc == 0 &&  d == EQ            = 0
    | rd == d || rd == EQ || d == EQ = dist - rdist
    | otherwise                      = rdist
    where mp = p1 - 1
          mc = mp - p2 + 1
          rd = 0 `compare` mc
          rdist = abs mc
          dist = 1 + 2 *
              | mc < 0 || rd == EQ && d == GT = s - mp - 1
              | otherwise = mp